The technology referred to as “e-fuse,” combines software algorithms and microscopic electrical fuses to produce chips able to regulate and adapt to their own actions in response to changing conditions and system demands. More specifically, an e-fuse reroutes chip logic, much the way highway traffic patterns can be altered, by opening and closing new lanes. The use of an e-fuse plays an important role in the post-fabrication personalization of microelectronic circuitry.
The e-fuse technology constantly monitors chip functionality and initiates corrective actions by tripping or blowing inexpensive, simple electrical fuses that are designed into the chip. The blown fuses help the chip to control individual circuit speed, manage power consumption, and repair unexpected, and potentially costly flaws. E-fuses may be used to invoke redundancy, to remove or replace defective bits in memory, or to permanently select certain regions of circuitry to personalize chips for specific applications.
It is important that e-fuses function flawlessly with appropriate values of pre-blow and post-blow resistance. In order to verify the proper operation of an e-fuse, characterization is achieved by measuring current-voltage characteristics of the fuse, then blowing the e-fuse and measuring the current-voltage characteristics of the fuse again. In order to blow the e-fuse a controlled amount of current is delivered to the fuse for a fixed amount of time, with specific control over the rise and fall times of the current. More specifically, the fuse blowing process requires the application of a pulse having fast rise and fall times and a duration of one to a few hundred microseconds. Rise and fall times are preferably on the order of 100 picoseconds. Appropriate test structures may be incorporated into chip designs in order to allow for the monitoring of fuse properties, such as the pre-blow and post-blow resistance.
Presently, the characterization of e-fuses requires a functional tester or a sophisticated external pulse generator unit, along with an appropriate wide-bandwidth probe card. In using a functional tester, the function of characterizing e-fuses must compete for the resources of the functional tester with a wide spectrum of traditional functional test and debug work. At best, functional testing is performed on a small sampling of the hardware, although the feedback for manufacturing and development purposes is not immediate. Alternatively, the incorporation of pulse generator units and wide bandwidth probe cards for every inline parametric tester is very expensive.